As noted by Engadget, the device will have support for AT&T network thanks to the quad-band HSPA support but the lack of AWS band means it would not work on the T-Mobile network.
If you never heard of the Xperia ray, it is Sony Ericsson's upcoming Android smartphone that was announced last month, having a slim 9.4mm body and just 100g weight. The device packs in a 3.3 inch TFT display with 854 x 480 resolution, 8 megapixel camera with auto-focus and LED flash and 720p video recording, 1Ghz Snapdragon processor and Android 2.3 Gingerbread operating system. The phone is slated to release sometime around August for around US $555.
For now check out the images clicked by FCC.
